public class e4_13 {
  public static void main(String args[]){
   Circle circle = new Circle();
  circle.setRadius(196.87);
  Tixing lader = new Tixing(3,21,9);
  Student zhang = new Student();
  System.out.println("zhang计算的圆的面积:");
  double result =zhang.computerArea(circle);
  System.out.println(result);
  System.out.println("zhang计算梯形的面积:");
  result = zhang.computerArea(lader);
  System.out.println(result);
}
}
